3. REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Feb. 29, 2020	Feb. 28, 2019	Feb. 29, 2020	Feb. 28, 2019
Net sales	$ 6,111	$ 3,163	$ 18,518	$ 13,814
Systems
Net sales	2,138	404	8,099	5,922
Contactors
Net sales	3,094	1,445	7,790	3,541
Services
Net sales	879	1,314	2,629	4,351
Wafer-level
Net sales	5,408	2,046	16,570	8,240
Test During Burn-In
Net sales	$ 703	$ 1,117	$ 1,948	$ 5,574

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

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